Ammonite Zones Research Articles

On the occurrence of rare nannoliths (calcareous nannofossils) in the Early Jurassic and their implications for the end‐Triassic mass extinction

AbstractA peculiar record of previously undescribed and/or rarely described nannoliths from the Hettangian to lower Pliensbachian of the Llanbdr (Mochras Farm) core, Wales (UK) is documented here. Some of the observed morphotypes are assigned to didemnid ascidians, commonly observed in the upper Rhaetian, as evidence of the resilience of ascidian tunicates during the end‐Triassic mass extinction. One newly described nannolith present throughout the Hettangian and Sinemurian,Quadrifolium hesselboi, is similar to forms previously observed in the upper Rhaetian, and is therefore considered to be a new nannofossil survivor from the end‐Triassic mass extinction. High‐amplitude changes observed in the absolute and relative abundances of nannoliths, schizosphaerellids and coccoliths across the Hettangian suggest a recovery interval from the end‐Triassic crisis spanning theplanorbis–liasicusammonite zones in four distinct steps with high volatility in environmental conditions, followed by the establishment of more stable environmental conditions in theangulataammonite zone.

Boreal Toarcian Biochronological Zonation by Bivalves of the Genus <i>Meleagrinella</i> Whitfield, 1885

Based on the chronological sequence of species of the bivalve genus Meleagrinella Whitfield, 1885 (family Oxytomidae Ichikawa, 1958) established in the Toarcian deposits of Northeast Russia, Eastern Siberia, and South Germany, a biochronological scale of the Lower Toarcian is proposed. Three oxytozones corresponding to Boreal ammonite zones are established: Meleagrinella golberti Oxytozone = Tiltoniceras antiquum and Harpoceras falciferum zones; Meleagrinella substriata Oxytozone = Dactylioceras commune Zone; Meleagrinella prima Oxytozone = Zugodactylites braunianus and Pseudolioceras compactile zones. Using the proposed zonation, an interregional correlation of sections of the Lower Toarcian of the North-East of Russia (Astronomicheskaya, Saturn, Brodnaya, Start rivers), Eastern Siberia (Anabar Bay, Markha, Tyung, Vilyui, Kelimyar, Motorchuna, wells of the Vilyui syneclise) and South Germany (the Ludwig Canal) is performed.

Integrated stratigraphy and clay mineralogy of the Owadów–Brzezinki section (Lower–Upper Tithonian transition, central Poland): implications for correlations between the Boreal and the Tethyan domains and palaeoclimate

New microfossil and magnetostratigraphical data as well as geochemical and clay mineral weathering indices are documented from the uppermost Jurassic Owadów–Brzezinki palaeontological site in central Poland. The newly discovered chitinoidellid assemblage of the lowermost part of the section and the previously documented assemblage from the middle part of the section are assigned, respectively, to the uppermost Dobeni and Boneti Subzones of the Chitinoidellidae Zone. The same part of the succession is correlated to the magnetosubzone M20n.2n. The new data allow refinement of the Tithonian stratigraphical scheme including an assignment of the upper part of the Boreal Zarajskites Subzone of the Scythicus (Panderi) ammonite Zone to the Upper Tithonian and its correlation with the lowermost part of Tethyan Microcanthum ammonite Zone and the lower portion of the M20n.2n magnetosubzone. The data show that the Fittoni/Albani ammonite zone boundary should likely be placed within the Boneti Subzone. The geochemical data show decreasing chemical weathering intensity during the earliest Late Tithonian in central Poland, which is linked to aridification of the latest Jurassic climate. The same trend is observed in coeval sections of NW and NE Europe. Supplementary material: Additional rock magnetic results, correlation of magnetic proxies with Al. and X-ray diagrams for clay minerals are available at https://doi.org/10.6084/m9.figshare.c.6299266

Non-avian theropod phalanges from the marine Fox Hills Formation (Maastrichtian), western South Dakota, USA.

We report here the first dinosaur skeletal material described from the marine Fox Hills Formation (Maastrichtian) of western South Dakota. The find consists of two theropod pedal phalanges: one recovered from the middle part of the Fairpoint Member in Meade County, South Dakota; and the other from the Iron Lightning Member in Ziebach County, South Dakota. Comparison with pedal phalanges of other theropods suggests strongly that the Fairpoint specimen is a right pedal phalanx, possibly III-2, from a large ornithomimid. The Iron Lightning specimen we cautiously identify as an ornithomimid left pedal phalanx II-2. The Fairpoint bone comes from thinly bedded and cross-bedded marine sandstones containing large hematitic concretions and concretionary horizons. Associated fossils include osteichthyan teeth, fin spines and otoliths, and abundant teeth of common Cretaceous nearshore and pelagic chondrichthyans. Leaf impressions and other plant debris, blocks of fossilized wood, and Ophiomorpha burrows are also common. The Iron Lightning bone comes from a channel deposit composed of fine to coarse sandstone beds, some of which contain bivalves, and a disseminated assemblage of mammal teeth, chondrichthyan teeth, and fragmentary dinosaur teeth and claws. We interpret the depositional environment of the two specimens as marginal marine. The Fairpoint bone derives from a nearshore foreset setting, above wave base subject to tidal flux and storm activity. The Iron Lightning specimen comes from a topset channel infill probably related to deposition on a tidal flat or associated coastal setting. The taphonomic history and ages of the two bones differ. Orthogonal cracks in the cortical bone of the Fairpoint specimen suggest post-mortem desiccation in a dryland coastal setting prior to transport and preservation in the nearby nearshore setting described above. The pristine surface of the Iron Lightning specimen indicates little transport before incorporation into the channel deposit in which it was found. The Fairpoint bone bed most probably lies within the Hoploscaphites nicolletii Ammonite Zone of the early late Maastrichtian, and would therefore have an approximate age of 69 Ma. The Iron Lightning bone is from the overlying H. nebrascensis Ammonite Zone, and is thus about one million years younger.

Biometry and biostratigraphy of the Early Cretaceous belemnite genus Castellanibelus from the southeast of France

Early Cretaceous deposits (Berriasian–Albian) crop out over large areas in the Vocontian Basin (VB, southeast of France). The important exposures have provided rich marine fossil faunas, including many specimens of ammonites and belemnites over the last 200 years. From the early 19th century onward, the definition of Lower Cretaceous belemnite species from the VB was essentially based on descriptive, qualitative approaches. This resulted in a variety of morphologically very closely related species, sometimes difficult to differentiate between each other. Biometric data and their statistical analysis offer a mathematical and objective framework to clearly delineate and define morphological species, especially when consecutive belemnite assemblages are continuously available from different stratigraphic levels. The present study is based on the analysis of 1762 specimens of Castellanibelus collected by ammonite zones and subzones across the entire Valanginian interval of the VB. Biometric data of this genus have been statistically analyzed and used to define four species, including one new to science: Castellanibelus orbignyanus, Castellanibelus vaubellensis, Castellanibelus suborbignyanus, and Castellanibelus toucasi sp. nov.

An expanded Smithian–Spathian (Lower Triassic) boundary from a reefal build‐up record in Oman: implications for conodont taxonomy, high‐resolution biochronology and the carbon isotope record

AbstractSome 2.7 myr after the Permian–Triassic boundary mass extinction, a stepwise extinction of the nekton (ammonoids and conodonts) ended at the Smithian–Spathian boundary (SSB) during an episode of climate cooling. SSB records from continental shelves are usually affected by an unconformity, suggesting a forced regression of glacio‐eustatic origin. Here, we document a new 30‐m‐thick SSB section from Jebel Aweri (Batain Plain, Oman) that provides an exceptionally complete and expanded record preserved in an exotic block. Most of this SSB section consists of microbial boundstone build‐ups with a framework of metazoan bioclasts that formed in shallow water on an offshore seamount. In Wadi Musjah (Hawasina nappes, Oman), another exotic block records the SSB in a deeper water setting represented by Hallstatt‐type facies. These two sections provide a unique perspective on the early Spathian rapid re‐diversification of conodonts. They led to a thorough revision of conodont taxonomy around the SSB and to the construction of the highest resolution biochronological scheme for this time interval in the Tethys. A total of five SSB sections from Oman representing both offshore seamounts and lower slope deposits were included in a high‐resolution, quantitative unitary associations (UA) analysis. The resulting 8 conodont biozones are intercalibrated with ammonoid zones and with the carbonate carbon isotope record ultimately placing the SSB in the interval of separation between UAZ3and UAZ4. Only the association ofNovispathodus pingdingshanensiswithIcriospathodus crassatuscan be used to unambiguously characterize the base of the Spathian.

Degree of Pyritization (DOP) and Indicator of Anoxicity (IA) in Jurassic sedimentary rocks from Bulgaria

The Degree of Pyritization (DOP) and the Indicator of Anoxicity (IA) were used as tools to assess the degree of redox conditions in Lower and Middle Jurassic strata from Bulgaria. Normally-oxygenated (with DOP values < 0.45 and IA values < 0.4), oxygen-restricted (0.45 < DOP < 0.7; 0.4 < IA < 0.5), and oxygen-depleted (DOP > 0.7 and IA > 0.5) bottom-water conditions were recognized on a selection of samples, mainly from the Ozirovo Formation (upper Pliensbachian–Toarcian), but also from the Etropole Formation (lower Bajocian). DOP and IA yielded the highest values (> 0.9 for DOP and > 0.5 for IA) from samples of the lower Toarcian Tenuicostatum and Falciferum ammonite zones, and thus, denoted declined oxygen levels and enrichment of reactive Fe at the sea floor. Beyond this stratigraphic level, both parameters indicated for prevailing normally-oxygenated to oxygen-restricted setting, with limitedly imposed environments beneath stratified water-column.

A Unitary Association-based conodont biozonation of the Smithian–Spathian boundary (Early Triassic) and associated biotic crisis from South China

The Smithian–Spathian boundary (SSB) crisis played a prominent role in resetting the evolution and diversity of the nekton (ammonoids and conodonts) during the Early Triassic recovery. The late Smithian nektonic crisis culminated at the SSB, ca. 2.7 Myr after the Permian–Triassic boundary mass extinction. An accurate and high-resolution biochronological frame is needed for establishing patterns of extinction and re-diversification of this crisis. Here, we propose a new biochronological frame for conodonts that is based on the Unitary Associations Method (UAM). In this new time frame, the SSB can thus be placed between the climax of the extinction and the onset of the re-diversification. Based on the study of new and rich conodont collections obtained from five sections (of which four are newly described here) in the Nanpanjiang Basin, South China, we have performed a thorough taxonomical revision and described one new genus and 21 new species. Additionally, we have critically reassessed the published conodont data from 16 other sections from South China, and we have used this new, standardized dataset to construct the most accurate, highly resolved, and laterally reproducible biozonation of the Smithian to early Spathian interval for South China. The resulting 11 Unitary Association Zones (UAZ) are intercalibrated with lithological and chemostratigraphical (δ13Ccarb) markers, as well as with ammonoid zones, thus providing a firm basis for an evolutionary meaningful and laterally consistent definition of the SSB. Our UAZ8, which is characterized by the occurrence of Icriospathodus ex gr. crassatus, Triassospathodus symmetricus and Novispathodus brevissimus, is marked by a new evolutionary radiation of both conodonts and ammonoids and is within a positive peak in the carbon isotope record. Consequently, we propose to place the SSB within the separation interval intercalated between UAZ7 and UAZ8 thus leaving some flexibility for future refinement and updating.

Early Jurassic coccolith diversification and response to pre-Toarcian environmental changes: A perspective from the Paris Basin

The early Jurassic saw large fluctuations in global temperature, sea-level and bottom-water oxic conditions prior to the Toarcian-Oceanic Anoxic Event (T-OAE), in several oceanic basins of NW Europe. Links between such changes, ocean nutrient concentrations and progressively increasing abundance and diversity of calcareous nannoplankton remain unclear. We have investigated the early Jurassic nannofossil assemblages of the Paris Basin across the mid-Sinemurian to lowermost Toarcian. Comparisons to geochemical proxy data let us decipher evolutionary trends from paleoenvironmental responses, test paleoecological affinities of coccolith species and improve our understanding of paleoenvironmental changes. Despite a strong evolutionary trajectory of the coccolith assemblages, multivariate analyses allowed to identify taxa indicating cold (Parhabdolithus, Crucirhabdus, Crepidolithus pliensbachensis), open ocean (Mitrolithus elegans, Mitrolithus lenticularis, Crepidolithus crassus sensu lato, Crepidolithus granulatus (both variants), Crepidolithus crucifer) and high fertility conditions (placoliths: Bussonius, Lotharingius, Similiscutum novum, Similiscutum finchii). Our data support that: (1) stable cool conditions persisted through the Upper Sinemurian, (2) progressive warming and high sea-levels onsetting across the Sinemurian/Pliensbachian transition, persisting to the lower margaritatus ammonite zone (AZ) may have favored the evolution of placoliths, (3) a first significant increase in abundance of placoliths was triggered in the stokesi ammonite subzone (ASz) by elevated fertility levels which preceded immediately the late Pliensbachian organic matter preservation interval (OMPI), (4) the OMPI and remaining subnodosus ASz were characterized by warm temperatures but low fertility surface waters, (5) another large increase in abundance of placoliths suggests again higher fertility levels across the uppermost margaritatus AZ, spinatum cold event and lowermost Toarcian.

Stratigraphic Modelling of the Lower/Middle Oxfordian (Upper Jurassic) Outer Ramp Deposits from the NE Paris Basin (France)

We investigate herein the lateral and vertical lithological heterogeneities of the Lower/Middle Oxfordian deposits (“Terrain à Chailles” and “Marnes des Eparges” formations) in the north-eastern Paris Basin. This new detailed stratigraphic framework documents the evolution at high resolution of an outer ramp based on regional correlations in order to constrain the evolution of petrological properties between the clayey “Argiles de la Woëvre” Formation and the more calcareous “Marnes et Calcaires à Coraux de Foug Formation. The “Argiles de la Woëvre” Formation is targeted for the deep storage of nuclear waste in north-eastern France. Nine wells are correlated over the “Zone of Interest for Further Research” (ZIRA), defined by the French agency for radioactive waste management (Andra), with a resolution of 0.5–1.0 m. The architecture and the age control of these formations have been refined, revealing that the “Terrain à Chailles” Formation is characterised by a regular slightly inclined sedimentation gently deeping in the SW direction and shows a lithological evolution from silty claystones to an increased occurrence of its calcareous content towards the top (Lower Oxfordian, uppermost mariae and cordatum ammonite zones). The above “Marnes des Eparges” Formation, characterised by claystone limestone alternations, is assigned to the Middle Oxfordian (plicatilis ammonite zone), deposited during a slightly enhanced subsidence phase in the SE part of the basin and documented and associated with onlaps geometries on the more proximal areas. However, this change in geometry does not affect petrological properties over ZIRA, as this is not accompanied by lithological changes. The environmental factors controlling petrological heterogeneities over ZIRA are also discussed. The stepwise increase in the carbonate content and the decrease in the detrital content towards the Lower to Middle Oxfordian deposits was likely triggered by a climate change towards drier conditions, modulated by sea level changes on a ramp morphology. A major condensation phase encompassing most of the Lower Oxfordian cordatum ammonite zone is also highlighted. The occurrence of a maximum regressive surface associated with gentle slope topography is a probable trigger for condensation. Changes in geometries are, however, associated with the activity of the Metz Fault, which potentially had an influence on the subsidence rates of the basin at that time.

The Basque coastal sections of the K/T boundary – A key to understanding “mass extinction” in the fossil record

 lnvestigations at the K/T boundary section al Zumaya, northern Spain, underline the importance of this section in (1) establishing a Maastrichtian ammonite zonation and (2) in understanding "mass extinctions" in the fossil record. "Mass extinction" at the K/T boundary can be restricted to two groups of oceanic surface plankton. Ammonites and inoceramids exhibit a gradual decline through the late Cretaceous, as probably also do the Temperate belemnites and the bulk of involved vertebrates. Most of these groups disappear a long time before the boundary. Compared with the available environmental factors, the course of ammonite diversity through time perfectly parallels the course of global sea level changes. Times of high extinction rates (e.g. the era and system boundaries) coincide with times of maximum regressions, while the subsequent evolutionary radiations match with the new sea level rise. There is no need for any cosmic catastrophy to explain the decline of most invertebrate and vertebrate groups. Coeval with the short-time extinction of oceanic surface plankton at the boundary itself, the following environmental and depositional changes were observed: minor (positive as well as negative) changes in temperature, boundary clay sedimentation, enrichment of iridium and noble metals, occurrence of sanidium spheres and shocked quartz, and changes in carbon and strontium isotopes. Ali these events were used to support the Alvarez hypothesis of a cosmic impact at the boundary. But they are much easier explained by increasing explosive volvanicity which, on the other hand, might correlate also with the time-equivalent magnetic reversals.

Towards the ammonite zonation of the Jurassic/Cretaceous transition: new data from ammonitico rosso/biancone sections of the Transdanubian Range (Hungary)

Towards the ammonite zonation of the Jurassic/Cretaceous transition: new data from ammonitico rosso/biancone sections of the Transdanubian Range (Hungary)

Palaeoecological implications of stable isotope analyses of late Valanginian ammonites from central Poland

Analyses of δ18O and δ13C of original shells of late Valanginian (verrucosum to triptychoides ammonite zones) ammonites preserved in clay at localities in central Poland, and of some Berriasian samples from well cores have been carried out for the first time. Analyses of carbon stable isotope composition have revealed diverse values, representing vital effects rather than recording the palaeoenvironment. In turn, analyses of oxygen stable isotope composition in samples from the verrucosum and triptychoides ammonite zones clearly indicates the connection between particular species and stable isotope ratios, and thus palaeotemperature. The interpretation of ammonite palaeoecology in the present paper is based on estimated palaeotemperatures and supports other interpretations of ammonite behaviour, mainly based on functional morphology of shells. There are two main groups of ammonites associated with lower and higher temperatures. The first group of δ18 O values indicates lower palaeotemperatures. Genera analysed include Bochianites, Dichotomites and Prodichotomites; a nekto-benthic (demersal) habitat is suggested for these. The second group, characterised by higher palaeotemperatures, includes Saynoceras, Valanginites and Olcostephanus, with a suggested nektonic (or planktic) habitat (free-floating), Neohoploceras and Neocomites with a suggested nektonic habitat (free-swimming) and a seasonal migration from warmer (Tethys) to cooler waters of the Polish Basin or lived in the Polish Basin for several summer and winter seasons. Co-occurring bivalves, echinoid spines and scaphopods were analysed for comparison with results obtained from ammonites for a better overview of the palaeoenvironment. The estimated palaeotemperatures for the Polish Basin are between 12 and 13 °C (at the sea floor) to 21–24 °C (in the upper water column), while for the Tethys or summer surface waters of the Polish basin, these were in the range of 26–30 °C.

Ecological adaptation of marine floras and faunas across the Early Jurassic Toarcian Oceanic Anoxic Event – A case study from northern Germany

We present new, high resolution bio- and chemostratigraphic data (calcareous nannofossils, ammonites, δ13Corg) of the lower Toarcian from an outcrop (Hondelage) in northern Germany. The three data sets, which cover lithostratigraphically the uppermost Amaltheenton-Formation (upper Pliensbachian) and the lower part of the Posidonienschiefer-Formation (lower Toarcian), allow a calibration of the different stratigraphic schemes in ultra high resolution. They further shed light on the ecologic conditions controlling the assemblage composition and evolutionary patterns of calcareous nannofossils, ammonites and gastropods.The distinctive negative δ13Corg excursion (negative CIE, Jenkyns Event), which is part of the early Toarcian Oceanic Anoxic Event (T-OAE), falls lithostratigraphically into the lower part of the laminated black shales of the Posidonienschiefer facies. The lower part of the Jenkyns Event is marked by the first occurrences of the calcareous nannofossil species Carinolithus superbus crassus and Diductius constans. These two events are biostratigraphically assigned to the Tiltoniceras antiquum ammonite Biohorizon (uppermost Dactylioceras tenuicostatum ammonite Zone). The top of the Jenkyns Event has been assigned to the Cleviceras exaratum ammonite Biohorizon (Harpoceras serpentinum ammonite Zone) of the lower Toarcian. The last occurrence of the nannofossil species Biscutum grande lies in the middle part of the Jenkyns Event.Calcareous nannofossils, ammonite faunas and gastropods are discussed with respect to the environmental and climatic changes, which occurred across the Pliensbachian/Toarcian boundary interval and throughout the Jenkyns Event. The extreme impoverished nannofossil and ammonite assemblages of the uppermost Pliensbachian are interpreted in the context of a cooling, primarily affecting the calcareous shelled primary producers. The onset of the Jenkyns Event in the lower Toarcian post-dates this cooling and is related to a subsequent warming. This climatic shift caused a bloom of diverse opportunistic nannofossil and ammonite taxa in the lower Toarcian. Nannofossil abundance patterns were controlled by an increased nutrient availability. The rapid evolution of the ammonite genera Tiltoniceras, Eleganticeras and Cleviceras (family Hildoceratidae), which started in the lower part of the Jenkyns Event, is potentially related to their adaptation to a shallow water dwelling habitat. The mass occurrence of phylogenetically first holoplanktonic gastropods in the lower part of the Jenkyns Event is interpreted in the context of impoverished ocean water oxygenation, which in turn triggered the evolution of a new ecological strategy.

Tithonian-Hauterivian chronostratigraphy (latest Jurassic-Early Cretaceous), Mediterranean-Caucasian Subrealm and southern Andes: A stratigraphic experiment and Time Scale

New radioisotopic dates of Tithonian-Hauterivian strata in the Neuquén Basin significantly recalibrate Early Cretaceous numerical ages. In order to evaluate the implications of these revised ages, a graphic correlation experiment of twenty-three Andean Tithonian to Hauterivian sections integrated the ranges of 254 species, sequence boundaries, polarity chrons, and radioisotopic ages that compose the ANDESCS DB. This database accurately reproduces the order of Andean ammonite zones and places them in a relative metric scale of a composite reference section. The ranges in the ANDESCS DB were correlated with the LOK2016 DB that comprises Tithonian-Albian ammonites, calpionellids, nannofossils, and polarity chrons in Mediterranean-Caucasian Subrealm stage reference sections. In 2017 these ranges were calibrated to GTS2016 mega-annums (MA). Although most Andean ammonoids were endemic to the Indo-Pacific Subrealm, nannofossils, calpionellids and polarity chrons were present in both areas. This stratigraphic experiment correlates base Berriasian as defined in France within the Substeueroceras koeneni Zone. In Andean sections this boundary is correlated with the Crassicolaria/Calpionella zone boundary dated at about 141 Ma. The base of the Valanginian defined by Calpionellites darderi correlates with the Neocomites wichmanni Zone of the Neuquén Basin (NB) recalibrated at 139.50 Ma, which is confirmed by multiple dates in Argentina, Mexico, Tibet, and elsewhere. The base Hauterivian correlates with base of Holcoptychites neuquensis Zone in the NB recalibrated at 131 Ma. Top of Hauterivian is in the Sabaudiella riverorum Zone in the NB and is dated at 127 Ma below an unconformity. Previous cyclostratigraphic astrochronologic cycles are averaged and calibrate the duration of the Tithonian at 5.67 myr, the Berriasian at 5.27 myr, the Valanginian at 5.30 myr, and the Hauterivian at 5.60 myr. The age of each stage is recalibrated by adding revised durations to the most common age of base Valanginian of 139.5 Ma. These ages revise the Berriasian to Hauterivian stages time scale, and the ages of stage boundaries are on average 2.8 myr longer than proposed by the new Neuquén Basin radioisotopic dates.

New data on the stratigraphy and depositional environment of the Jurassic-Cretaceous boundary sediments of the northwestern part of the Yenisei-Khatanga trough

Research subject. Boundary Jurassic-Cretaceous sediments of the western part of the Yenisei-Khatanga Regional Trough. Materials and methods. The main correlation tools were seismostratigraphic, logging, and biostratigraphic methods. Litho- and biofacies methods were used to reconstruct the development conditions of the Yanovstan Formation and the NKh group of the Ryazanian Stage reservoirs. Results. The composition of macro- and microfauna complexes was defined, analogues of the ammonite and foraminiferal zones of the Upper Volgian substage and the Ryazanian stage of Siberia were established. The structure of the Upper Jurassic and Ryazanian complexes of the western part of the Yenisei-Khatanga Regional Trough was detailed. Conclusions were made about the formation conditions of the Volgian and Ryazanian deposits. Conclusions. The sediments were found to have been formed in a sea basin with stable salinity and low water energy, in relatively deep-water conditions. Mixed turbidite systems with multipoint supply sources were identified, in which the terrigenous material was supplied from southeast to northwest.

Une association d'ammonites rare dans la Zone à Romaniceras ornatissimum (Turonien moyen) du Massif d'Uchaux, Vaucluse, France

The Uchaux Massif (Vaucluse, SE France) is one of the rare places in Europe where ammonites collecting can be led from a high middle Turonian through Late Turonian. That incited Alcide d'Orbigny in 1852 to quote Uchaux as "the French type of the Turonian stage" to complement the Saumur, Tourtenay, Montrichard and Tours localities mentionned in 1842 when the stage was created. In 2014, the monograph by Robaszynski et al. synthetized and actualized the informations available on the litho- and biostratigraphy of the Turonian from the Uchaux Massif. More recently, a new outcrop at Mondragon, in a place named Prés Morel, exposes the whole carbonate siltstones with Spongia of the Peyras Member (UL3). Were collected : Lewesiceras peramplum (Mantell, 1822), Romaniceras (Romaniceras) marigniacum Amédro & Châtelier, 2020, R. (Yubariceras) ornatissimum (Stoliczka, 1864), R. (Y.) kanei Jones, 1938, Collignoniceras woollgari regulare (Haas, 1946), C. carolinum (Orbigny, 1841), C. papale (Orbigny, 1841), C. turoniense (Orbigny, 1841) and a new species of Collignoniceras : C. rhodanicum Amédro, Baudouin & Delanoy sp. nov. This assemblage, unprecedented in the studied area, is characteristic of the Romaniceras ornatissimum Zone which is the third of the four ammonite zones of the middle Turonian (Tm 3). At the top of this third zone, the surprise was to find the Romaniceras marigniacum bio-horizon defined in 2020 in the southern part of the Paris Basin at the top of the Tuffeau de Bourré and at the base of the Tuffeau Jaune de Touraine. Moreover, we now think that the Peyras Member has to be fully assigned to the Romaniceras ornatissimum Zone. Lastly, the assemblage includes a rich population of Collignoniceras carolinum (24 specimens), the most important known to-day over the world. All these ammonites allow to know the spectrum of their morphological variations and show a dimorphism through the existence of micro- and macroconchs.

Jurassic palynoevents in the circum-Arctic region

Successions of Jurassic strata located in the Arctic region normally yield rich assemblages of terrestriallyderived and marine palynomorphs, reflecting relatively warm air and sea-surface temperatures. The land plant floras were prone to the development of local communities and regional provincialism, whereas the marine biotas thrived across extensive open marine areas with high productivity, resulting in the rapid evolution of dinoflagellate cysts (dinocysts) following their earliest fossil record in the Triassic. Dinocysts exhibit low taxonomic richness and provide low biostratigraphic resolution throughout the Lower Jurassic sections. By contrast, they are diverse in Middle and Upper Jurassic strata where they provide excellent biostratigraphic markers for correlating and dating both surface and subsurface sections. Over twenty formal and informal biozonations based on the firstand last occurrences of dinocysts have been erected in Alaska, Arctic Canada, the Barents Sea region, Greenland and northern Russia, many of which are correlated with macrofossils, including ammonites, that occur in the same sections. This paper presents a compilation of 214 Jurassic palynostratigraphic events (118 first occurrences and 96 last occurrences) that have regional chronostratigraphic value in the Circum-Arctic, based on their published records. Each event is correlated with the base of a chronostratigraphical unit (including formal stages and sub-Boreal ammonite zones), or as an estimated percentage above the base of the chronostratigraphical unit relative to the entire unit. The relationships of each event to stages and key fossil zonal schemes is shown on chronostratigraphic plots using the 2020 version of TimeScale Creator®.

Latest Olenekian (Early Triassic) Ammonoids from the Uppermost Part of the Osawa Formation (Inai Group) in the South Kitakami Belt, Northeast Japan

The Osawa Formation of the South Kitakami Belt is correlated with the upper Olenekian (Lower Triassic) based on its rich ammonoid fauna. Although two ammonoid zones, the Subcolumbites Zone below and Arnautoceltites Zone above, were established in the formation, its uppermost part has been almost barren of ammonoids. An “Olenekian–Anisian mixed” ammonoid fauna found from the uppermost Osawa Formation at Asadanuki, comprising eight genera, is the only one representing the uppermost part. It is unique in the generic composition and new ammonoid zone, the Eodanubites Zone, is proposed in the uppermost part of the Osawa Formation. The fauna consists of typical Olenekian genera such as Pseudosageceras, Ceccaisculitoides, Procarnites and Eodanubites, the Olenekian–Anisian genus Leiophyllites and Keyserlingitidae, and “Anisian” genera Japonites and Procladiscites. The last two genera, however, actually range down into the uppermost Olenekian, and therefore, based on the ammonoids, the Eodanubites Zone is considered to be latest Olenekian in age. This fauna is similar to the uppermost Olenekian Ziyun fauna in Guizhou, South China, and the Eodanubites Zone is correlated with the uppermost Olenekian Deslicairites Beds of Romania and the Neopopanoceras haugi Zone of Nevada.

New insights into the Barremian–lower Aptian calcareous nannofossils of the Mediterranean Tethys: Chronostratigraphic and paleobiogeographic implications

A detailed study of calcareous nannofossil assemblages from twelve uppermost lower Barremian–lower Aptian sections in the Subbetic Domain of the Betic Cordillera was performed. Seven new nannofossil species (Crucibiscutum bastetanum, Crucibiscutum gracile, Chiastozygus lamprostauros, Cyclagelosphaera platyaspis, Lithraphidites aichmoides, Lithraphidites pugio, and Rhagodiscus sicutclipeus) are described, one species is emended (Lithraphidites magnus) and the taxonomic concept of the marker species Hayesites irregularis is discussed and clarified. The detailed stratigraphic ranges of the new species, together with those of other relevant taxa, are determined and correlated to standard ammonite biostratigraphy. Age estimates of biostratigraphically relevant calcareous nannofossil biohorizons are calculated using astrochronologically tuned cyclostratigraphic data. Five new calcareous nannofossil subzones are proposed which enhance upper Barremian biostratigraphic resolution at a regional scale and are directly correlated with respect to the standard Tethyan ammonite zonation. Two of the new species described here are used as biostratigraphic markers for the newly proposed subzones. The duration of each subzone is provided through astrochronological calibration. This study allows the refinement of the calcareous nannofossil zonation for the Mediterranean–Atlantic province of the Tethyan Realm. The implications of these new results are discussed regarding the extant definition and use of the Barremian/Aptian boundary. The morpho-evolutionary trends of selected nannofossil groups are reviewed in relation to the latest Barremian–Aptian paleogeographic changes, showing these were a prominent factor controlling calcareous nannoplankton evolution and biogeographical distribution in the west European-Atlantic region.